The present invention relates to medical devices, systems and methods, and, more particularly, to a method and system for diagnosing pulmonary congestion in a mammalian heart.
Pulmonary congestion is a condition that affects thousands of people throughout the world. Pulmonary congestion may be described as the inability of the heart to pump blood at an adequate rate in response to the filling pressure. Such a condition can have many consequences, including congestion in the tissues, peripheral as well as pulmonary edema, and shortness of breath. In its most severe stages, congestive heart failure results in death.
For this reason, many approaches to treating pulmonary congestion have been tried. These past attempts include electrical stimulation as well as drug therapy or both in combination. See for example, U.S. Pat. No. 5,213,098 to Bennett et al. (electrical stimulation) or U.S. Pat. No. 5,405,362 to Kramer, U.S. Pat. No. 4,360,031 to White, U.S. Pat. No. 3,923,060 or 4,003,379 to Ellinwood (electrical stimulation and drug therapy).
To date drug therapy is the method of treatment that has enjoyed the greatest success. Such drug therapies include, for example, diuretic agents and angiotens in converting enzyme inhibitors. One particular method, which has been found to be somewhat effective in reducing the symptoms of pulmonary congestion, is intermittent administration of nitroglycerin to the body.
Although various drug therapies may be effective in select patients, in many cases such a treatment has limited effectiveness or is difficult to administer or both. For example, nitroglycerin is only effective if administered at the appropriate and may also lead to a number of side effects including hypotension; administration of nitroglycerin also usually requires physician supervision.
Attempts have been made to use external impedance measuring systems to detect ischemia, which can lead to pulmonary congestion. For example, Kun et al., U.S. Pat. No. 5,807,272 discloses an impedance spectroscopy tissue status monitoring and measurement system. Likewise, Dzwonczyk et al., U.S. Pat. No. 5,454,377 discloses a method for measuring the complex impedance spectrum of a portion of the myocardium. However, both inventions do not measure the trans-thoracic impedance of the patient. U.S. Pat. No. 5,282,840 to Hurdlik discloses a physiological monitoring system for monitoring the condition of a patient""s body tissue. U.S. Pat. No. 6,104,949 to Pitts-Crick and Van Oort, discloses a device and method useful in the diagnosis and treatment of congestive heart failure, which senses trans-thoracic impedance as well as patient posture and is incorporated herein by reference.
Thus it would be desirable to provide a way to detect and quantitatively monitor the degree of pulmonary congestion. Such a quantitative monitor should be sensitive to early changes of pulmonary congestion, should be both easy and convenient to use, and should require little or no physician supervision. It would also be desirable to provide an automatic method and device for treating pulmonary congestion that uses such a quantitative monitor.
As discussed above, the most pertinent prior art patents are shown in the following table:
All the patents listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.
The present invention is therefore directed to providing a method and system for diagnosing and/or measuring ischemia and/or pulmonary congestion. The system of the present invention overcomes at least some of the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of diagnosing, monitoring and measuring pulmonary congestion based on trans-thoracic impedance values.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the pacing of cardiac tissue. Those problems include, without limitation: (a) difficulty in detecting pulmonary congestion in a patient (b) difficulty in quantitatively determining the degree of pulmonary congestion in a patient; (c) difficulty in monitoring the change in pulmonary congestion in a patient over time; (d) need for physician supervision in monitoring pulmonary congestion; (e) difficulty in responding to pulmonary congestion with appropriate therapy.
In comparison to known pacing techniques, various embodiments of the present invention provide one or more of the following advantages: (a) the ability to quantitatively determine the degree of pulmonary congestion in a patient; (b) the ability to monitor pulmonary congestion in a patient over time; (c) the ability to use trans-thoracic impedance values to diagnose pulmonary congestion; (d) the ability to determine trans-thoracic impedance values and exercise level values in a patient; (e) reduced amount of physician supervision in monitoring pulmonary congestion; and (f) the ability to treat pulmonary congestion in a patient based on determined trans-thoracic impedance values.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of quantitatively determining the degree of pulmonary congestion in a patient; (b) an IPG capable of using trans-thoracic impedance values to diagnose pulmonary congestion; (c) an IPG capable of monitoring pulmonary congestion; (d) an IPG capable of treating pulmonary congestion; (e) methods of determining the degree of pulmonary congestion in a patient based on impedance values; and (f) methods of diagnosing and treating pulmonary congestion based on impedance values.
At least some embodiments of the present invention involve sensing at least one decrease in a trans-thoracic impedance value from a baseline trans-thoracic impedance value. At least one increase in a heart rate value from a baseline heart rate value is also sensed. Pulmonary congestion is diagnosed if the decrease in the trans-thoracic impedance value corresponding to the increase in the heart rate does not increase after a predetermined interval. The baseline trans-thoracic impedance value, trans-thoracic impedance value, heart rate and predetermined interval may all be determined. In some embodiments of the invention, the trans-thoracic impedance value may be determined by delivering an excitation current pulse between a first electrode and a second electrode and sensing the trans-thoracic impedance between the two electrodes. In some embodiments of the invention, the degree of pulmonary congestion may be determined and appropriate therapy may be delivered.